1. Field of the Invention
The present invention relates to skimming mechanisms, in particular, a skimming mechanism for use in the removal of scum from water in wastewater treatment.
2. Description of the Prior Art
Wastewater created by residential and industrial uses of water must be cleaned before the water can be reintroduced into the environment or else toxicity problems arise. Water treatment plants treat wastewater by several different processes in order to remove wastes from water. Clarification is a process used to remove sedimentation and scum from wastewater. Clarifier tanks are commonly used to accomplish clarification.
High volumes of scum may be removed from wastewater by using a cylindrical clarifier tank equipped with an extended scum trough. Conventional radially oriented skimmers are rotated across the surface of wastewater contained in the tank. The skimmers rotate across the scum trough, which extends inwards from the edge of the tank, and deposit the scum into the scum trough. The scum is removed from the scum trough through piping which extends out of the clarifier tank.
A conventional scum trough has large trough beaches extending on both sides of the trough mouth into which the scum is deposited. The trough beaches slope upwards from the surface of the wastewater to the trough mouth so that the trough beaches may elevate the skimmers to the trough mouth. The skimmers rotate across the trough beaches as the skimmers approach and depart the scum trough. In order to retain accumulated scum on the skimmers the leading edge of the trough beach should be located parallel to a skimmer encountering the beach so the entire length of the skimmer is simultaneously elevated by the surface of the trough beach to the trough mouth. Furthermore, in order to smoothly lower the skimmer from the trough mouth to the surface of the wastewater the surface of the trailing trough beach should also be parallel to the skimmer. The trough beaches required for conventional radially oriented skimmers must be quite large in order to extend parallel to a skimmer from the leading edge of the trough to the trailing edge of the trough. Typical conventional scum troughs are substantially pie shaped.
Conventional radially oriented skimmers and conventional scum troughs suffer some disadvantages. The large scum troughs required for radially oriented skimmers are very heavy. The trough beaches must be ribbed for structural strength due to the weight of the trough. However, the ribs disrupt the smooth surface of the beaches and interfere with the beach-skimmer contact necessary for proper scum and fluid removal. Furthermore, ballasts must typically be added beneath the beaches to help keep the heavy troughs afloat. However, the heavy semi-flotation scum trough is subject to becoming unmoored within the clarifier tank by pulsation and fluctuation of the water surface whenever there is a high wind. In addition, the radially oriented skimmers are subject to scum escaping around the ends of the skimmers.